Increases in the recording densities on magnetic recording media continue to occur at a remarkable rate, and in order to meet future demands for further increases in recording density, further miniaturization of the magnetic heads must be achieved.
For example, in the read portion (the head portion used for reading) of a magnetic head, not only must a fine resist pattern (isolated pattern) be formed, thereby enabling the formation of a fine magnetic film pattern, but the shape of this magnetic film pattern must be close to being substantially rectangular.
Normally, the production of fine structures within the read portion of a magnetic head uses a method in which the magnetic film is subjected to ion etching, and an example of this method is described below. Ion milling is a widely used form of ion etching. FIG. 1A through FIG. 1E show schematic illustrations (side sectional views) of each of the steps in the formation of an electrode using typical ion milling and sputtering.
First, as shown in FIG. 1A, a magnetic film 2′ is laminated on top of a substrate 1, and a base film 3′ that is soluble in alkali developing solution, and a resist film 4′ are then laminated sequentially on top of the magnetic film 2′. Subsequently, selective irradiation is conducted through a mask pattern from above the resist film 4′, using a light source such as i-line radiation or a KrF excimer laser. Alkali developing is then conducted, thereby dissolving certain areas of the resist film 4′ (the exposed portions in the case of a positive resist, or the unexposed portions in the case of a negative resist), and generating a resist pattern 4 with a substantially rectangular cross section. At this point, the base film 3′ positioned below those portions of the resist film 4′ removed by the alkali developing is also removed by the developing solution, and because the base film 3′ has a higher level of alkali solubility than the resist film 4′, the alkali developing generates a lift-off pattern 5 such as that shown in FIG. 1B, which includes a base film 3′ pattern 3 of narrow width, and a resist pattern 4 of the resist film 4′ of greater width.
When ion milling is then conducted using this pattern 5 as a mask, then as shown in FIG. 1C, the magnetic film 2′ surrounding the pattern 5 is etched away, forming a magnetic film pattern 2 beneath the pattern 5 and in the immediate vicinity thereof.
When sputtering is then conducted, an electrode film 6 is formed on top of the pattern 5, and on top of the substrate 1 in the vicinity of the magnetic film pattern 2, as shown in FIG. 1D.
Finally, when an alkali developing solution is then used to dissolve the pattern 3 of the base film 3′, the resist pattern 4 of the resist film 4′ is removed, and a magnetic head 10 such as that shown in FIG. 1E, including the substrate 1, the magnetic film pattern 2 of a predetermined width formed on top of the substrate 1, and the electrode film 6 formed surrounding the pattern 2, can be obtained.
On the other hand, for the write portion (the head portion used for writing) of a magnetic head, a technique is used wherein a fine trench-like resist pattern is formed, and this resist pattern is then used as a frame to conduct plating, thereby forming a fine magnetic film pattern, as shown in FIG. 2A through FIG. 2C (side sectional views).
In other words, first, as shown in FIG. 2A, a plating seed layer 11 is formed on the upper surface of a base material (not shown in the figures), which includes a predetermined laminated structure formed on top of a substrate, and conventional lithography such as that described above is then used to form a slit-shaped resist pattern 12 with a substantially rectangular cross section on top of the plating seed layer 11.
Next, as shown in FIG. 2B, plating is conducted within the trench portion (concave portion) enclosed by the resist pattern 12, thus forming a magnetic film 13′.
Subsequently, as shown in FIG. 2C, the resist pattern 12 is removed, generating a magnetic film pattern 13 with a substantially rectangular cross section.
The patent reference 1 listed below proposes a method of forming a taper-shaped resist pattern using a non-chemically amplified novolak-based positive resist composition.
[Patent Reference 1]
Japanese Unexamined Patent Application, First Publication No. 2002-110536
In the read portion of a magnetic head, as shown in FIG. 1A through FIG. 1E, if ion milling is conducted using a pattern 5 in which the resist pattern 4 is substantially rectangular (hereafter, this type of resist pattern is also referred to as simply a “rectangular resist pattern”), then the anisotropy of the ion milling causes the printed magnetic film pattern 2 to be converted to a shape with a trapezoidal (tapered) cross section that widens with increasing proximity to the substrate 1, as shown in FIG. 1C. With this type of trapezoidal shape, that is, a trapezoidal shape in which the angle (θ1 in FIG. 1C) is large, a fine pattern cannot be produced in the magnetic film, meaning when used as the read portion of a magnetic head, the level of reading noise tends to increase. As a result, a method that enables the shape of the magnetic film to be shifted closer to a rectangular shape, that is, enables the value of θ1 to be reduced, has been keenly sought.
On the other hand, in the write portion of a magnetic head, if the magnetic film pattern 13 is a rectangular shape, then increasing the magnetic recording density is difficult, and consequently there is considerable demand for forming the side walls of the magnetic film pattern in an inverted taper shape, as shown by the dashed lines in FIG. 2C.
In the method disclosed in the patent reference 1 listed above, a non-chemically amplified resist is used, and exposure treatment is conducted with a shift in the depth width of focus, thereby forming the resist pattern with a tapered shape. However, if this method is applied to a chemically amplified resist, then the resolution of the resist pattern is inadequate, and the depth width of focus is also inadequate, meaning a taper-shaped resist pattern cannot be stably reproduced. Accordingly, if ion milling or plating are then conducted using such a resist pattern, then a number of problems can arise, including an inability to form a fine magnetic film pattern, fluctuations in the size of the magnetic film pattern on the substrate, and fluctuations in the angle of inclination (θ2′ and θ3′ in the following description) of the side walls of the magnetic film pattern on the substrate.